The present invention relates generally to the field of hierarchical storage management, and more particularly identification and migration of hot and cold data blocks.
In the field of hierarchical storage, a logical volume is formed by data blocks. In a hybrid storage system, each block may be located on a different type of storage device, such as a solid-state drive or a magnetic hard drive, for example. Storage tiers, made up of the different types of storage devices, are defined based on the device characteristics. Users configure their storage system, based on certain considerations such as workload, performance, capacity and cost requirements.
Automated storage tiering (sometimes herein referred to as auto-tiering) is automated promotion or demotion of data blocks, or extents, across different tiers of storage devices and media. A block (an “extent”) is a contiguous area of storage reserved for a file, or a portion thereof, in a file system. As used herein, an extent and a block are synonymous and the terms may be used interchangeably. Different tiers (types) of storage device operate with different speeds, latencies and costs. A block that is accessed more often (a block having high “heat”) may be stored on a higher tier that may be faster but scarcer and more expensive, while a block that is accessed less often may be stored on a lower tier that may be slower but more plentiful and less expensive. Other considerations (for instance, required security level) may also be used in assigning certain extents to a given tier.